Abstract: We study the properties of strain bursts (dislocation avalanches) occurring
in two-dimensional discrete dislocation dynamics models under quasistatic
stress-controlled loading. Contrary to previous suggestions, the avalanche
statistics differs fundamentally from predictions obtained for the depinning of
elastic manifolds in quenched random media. Instead, we find an exponent \tau
=1 of the power-law distribution of slip or released energy, with a cut-off
that increases exponentially with the applied stress and diverges with system
size at all stresses. These observations demonstrate that the avalanche
dynamics of 2D dislocation systems is scale-free at every applied stress and,
therefore, can not be envisaged in terms of critical behavior associated with a
depinning transition.